skin and soft tissue infections dermatophytes
TRANSCRIPT
Skin and soft tissue infections
Dermatophytes
Dr. Hala Al Daghistani
Dermatophytoses are superficial infections of the skin and its appendages,
commonlyknown as ringworm, athlete’s foot, and jock itch.
They are caused by species of the genera including:
Microsporum, Trichophyton, and Epidermophyton
They are collectively known asDermatophytes. These fungi are highly adapted to
the nonliving, keratinized tissues ofnails, hair, and the stratum corneum of the
skin(the outermost layer of the epidermis). The source of infection may be humans.
Agents of Superficial and Subcutaneous Mycoses FUNGUS INFECTION DISEASE
Dermatophytes Microsporum canis Hair,skin Ringworm
Microsporum audouini HairRingworm
Microsporum gypseum Hair, skin Ringworm
Trichophyton tonsurans Hair, skin, nails Ringworm
Trichophyton rubrum Hair, skin, nails Ringworm
Trichophyton mentagrophytes Hair, skin Ringworm
Trichophyton violaceum Hair, skin, nails Ringworm
Epidermophyton floccosum Skin Ringworm
Other superficial fungi Malassezia furfur Skin (pink to brown) Pityriasis (tinea) versicolor
Hortaea werneckii Skin (brown–black) Tinea nigra
Trichosporon cutaneum Hair (white) White piedra
Piedraia hortae Hair (black) Black piedra
Subcutaneous fungi Sporothrix schenckii Subcutaneous Sporotrichosis
lymphatic spread
Dermatophytes require a few days to a week or more to initiate growth.
Most grow best at 25°C on Sabouraud dextrose agar, which is usually used for culture.
The hyphae are septate, and their conidia may be borne directly on the hyphae or on
conidiophores.
Dermatophytoses are slowly progressive eruptions of the skin and its appendages, are not
painful or life threatening.
The manifestations (and names) vary depending on the nature of the inflammatory
response in the skin, but typically involve erythema, itching, and scaling.
The most familiar is “ringworm” which gets its name from the annular shape of creeping
margin on the advancing edge of dermatophyte growth.
EPIDEMIOLOGY
There are both ecologic and geographic differences in the occurrence of the
various dermatophytespecies. Some are primarily adapted to the skin of humans,
others to animals,and others to the environment. All may serve as the source for
human infection.
Human-to-human transmission usually requires close contact with an infected
subjector infected person or animal, because dermatophytes are of low infectivity
and virulence.Transmission usually takes place within families or in situations
involving contact with detachedskin or hair, such as barber shops and locker
rooms.
Pathogenesis
Dermatophytoses begin when minor traumatic skin lesions come in contact with
dermatophytehyphae shed from another infection. Susceptibility may be
enhanced by local factorssuch as the composition surface fatty acids.
Once the stratum corneum is penetrated,the organism can proliferate in the
keratinized layers of the skin aided by a variety of proteinases.
The course of the infection is dependent on the anatomic location, moisture,
thedynamics of skin growth and desquamation, the speed and extent of the
inflammatory response,and the infecting species. For example, if the organisms
grow very slowly in thestratum corneum, and a fast desquamation of this layer
occur, the infectionwill probably be short-lived and cause minimal signs and
symptoms. Immunosuppressiveagents such as corticosteroids decrease shedding of
the keratinized layersand tend to prolong infection.
Invasion of any deeper structures is extremely rare.
However, infection may spread from the skin to other keratinized structures,
such as hair and nails,or may invade them primarily. The hair shaft is penetrated
by hyphae and the end result is damage to the hair shaft structure, which
oftenbreaks off. Loss of hair at the root and plugging of the hair follicle with
fungal elementsmay result.
Invasion of the nail bed causes a hyperkeratotic, which dislodges ordistorts the
nail (Hyperkeratosis is thickening of the stratum corneumoften associated with
the presence of an abnormal quantity of keratin).
IMMUNITY
The great majority of dermatophyte infections pass through an inflammatory
stage tospontaneous healing.
Phagocytes are able to use oxidative pathways to kill the fungi,both
intracellularly and extracellularly.
Antibodies may be formed during infection, but play no known role in
immunity.
Most clinical evidence points to the importance of cell-mediatedimmunity
(CMI), as with other fungal infections.
Occasionally, dermatophyte infections become chronic and widespread.
Hair infection leads to itching and hair loss
Skin infection favors moist areas and skin folds
KOH mount of skin scrapingsand infected hairs demonstratethe presence
of hyphae. Culture (SDA) is used when KOH preparations arenegative
Subcutaneous fungi
Fungal pathogens can produce many subcutaneous manifestations as part
oftheir disease spectrum. Some are introduced traumatically through theskin
and involve mainly
1. Subcutaneous tissues
2. Lymphatic vessels
3. Contiguous tissues.
They rarely spread to distant organs.
The diseases they cause include:
Sporotrichosis داء الشعريات المبوغة( )
Chromoblastomycosis (الفطريات الاصطباغية)
Mycetoma)الورم الفطري(.
Only Sporotrichosis has a single specific etiologicagent, Sporothrix
schenckii. Chromoblastomycosis and Mycetoma are clinical syndromeswith
multiple fungal etiologies.
Sporotrichosis is a chronic infection characterized by nodular lesions of
Subcutaneous tissue and adjacent lymphatics that suppurate (make pus), ulcerate (digest
the tissue) and drain. There are several kinds of diseases that may be caused
by Sporothrix
lymphocutaneous infection: localized lymphocutaneous sporotrichosis
Osteoarticular sporotrichosis (bone and joints may be infected)
Keratitis (the eye may be infected)
Systemic infection
Pulmonary sporotrichosis (25% of cases).
Cutaneous sporotrichosis: This is the most common form of this disease.
Symptoms of this form include nodular lesions or bumps in the skin, at the
point of entry. The lesion starts off small and painless, and ranges in color from
pink to purple.
In nature, Sporothrix lives on wood, decaying vegetation (including rose
thorns), animal excreta and soil. Because ROSES can spread the disease, it is
one of a few diseases referred to as rose-thorn or rose-gardeners' disease.
Mycetoma الفطري الورم
Mycetoma is a clinical term for an infection associated with trauma to the foot
whichcauses inoculation of any of fungal species.
Most cases, however, occur in the tropics, probably because the chronically
damp,macerated skin of the feet that causes predisposition toward mycetoma. The
clinical features include: tumor like swelling, multiple drainage sinuses, grains in
sinuse(sclerotia,a mass of hyphal threads, capable of remaining dormant for long
periods).
Opportunistic infection
The most common opportunistic infections are caused bythe yeast Candida
albicans,a normal inhabitant of the gastrointestinal and genital floras,and a mold,
Aspergillus,commonly found in the environment.
Agents of Opportunistic Mycoses
Organism Tissue Source Infection Candida Yeast Endogenous Skin, mucous membranes, UT,
disseminated
Aspergillus Hyphae (septate) Environment Lung, disseminated
ZygomycetesHyphae (nonseptate) Environment Rhinocerebral, lung,disseminated
CANDIDA C. albicans grows in multiple morphologic forms, most often as a yeast with budding
C. albicans is also able to form hyphae triggered by changes inconditions such as
temperature, pH, and available nutrients. When observed in their initial stages when still
attached to the yeast cell, these hyphae look like buds and are called germ tubes.
Clinical manifestations
Candidiasis occurs in localized and disseminated forms. Localized disease is
seen as erythema and white plaques in moist skin folds (diaper rash) or on
mucosal surfaces(oral thrush). It may also cause the itching and thick white discharge of vulvovaginitis.
Deep tissue and disseminated disease are limited almost exclusivelyto the
immunocompromised.
EPIDEMIOLOGY
C. albicans is a common member of the oropharyngeal, gastrointestinal, and
female genitalflora.
Infections are endogenous except in cases of direct mucosal contact with
lesions in others (eg, through sexual intercourse).
Although C. albicans is a common cause of nosocomial infections, the fungi
are also derived more frequently from the patient’s ownflora than from
cross-infection.
Invasive procedures and indwelling devices may provide the portal of entry,
and the number of available Candida may be enhanced by the used of
antibacterial agents. Pathogenesis
The change from the yeast to the hyphal form is strongly associated with
enhanced pathogenic potential of C. albicans. The hyphae are seen only when
Candida starts to invade, either superficially or in deep tissues.
Hyphae secrete proteinases and phospholipases that are able to digest
epithelial cells and probably facilitate invasion
There is also evidence that C. albicans may be able to induce its own
phagocytosis by endothelial cells.
C. albicans has protein surface receptors that bind the C3 component of
complement thus prevent opsonization.
Clinical Manfestation
The Manfestation C. albicans skin infections occur in folds, and wet areas.
The initial lesions are erythematous papules or confluent areas associated
with tenderness, erythema, and fissures of the skin.
Infection usually remains confined to the chronically irritated area, but
mayspread beyond it, particularly in infants.
Chronic mucocutaneous candidiasis is associated with specific T-cell defects
DIAGNOSIS
Superficial C. albicans infections provide ready access to diagnostic
material.
Exudate or epithelial scrapings examined by potassium hydroxide (KOH)
preparations or Gram smear demonstrate abundant budding yeast cells
if associated hyphae are present, the infection is almost certainly caused by
C. albicans.
Cultures on SDA is critical for diagnosis